The Army will formally close Operation Banner - its 38-year anti-terrorist role - at midnight tonight.

The move is in recognition of the huge reduction in the security threat in recent years and is another marker signifying the end of the Troubles.

But at the same time, legislation goes into effect giving soldiers here the power to stop and question anyone about their movements - and hold them indefinitely until they answer.

People refusing to identify themselves or answer questions about their movements could be subject to a £5,000 fine.

The PSNI is also granted the power tonight - even though the Cabinet rejected them as unacceptable for police in the rest of the UK.

The Government acknowledged last night that the role of the Army will be " slightly different to that in the rest of the UK".

A spokesman for the Northern Ireland Office said the special powers are necessary because the Army could still be called up to support the PSNI.

But the move was questioned in some quarters.

"There's a definite irony in having the troops move out on July 31st and giving them powers for arrest on August 1," said Jane Winter, director of British- Irish Rights Watch. "On the face of it, there's no rationale for that."

The Committee on the Administration of Justice said the new power is " unacceptable", but Government defends it as a necessary preparation.

"We hope that it won't be necessary to have troops on the streets again, " an NIO spokes- person said, "but we must be prepared and as long as there is the potential for serious public order incidents, the Army should be available to support the police and this role requires the military to have powers over and above the ordinary citizen.

"Military support is not necessary for public order situations elsewhere in the UK, and therefore the powers are not required in England, Scotland or Wales."

Fewer than 5,000 troops are now stationed in Northern Ireland in 10 bases. The majority will not have any operational role, but will be involved in training or other preparations for operations abroad.

A small number of military people - bomb disposal experts and helicopter crews among them - will be active in Operation Helvetic, the new name for the Army's supporting role in the province.

DUP MP Jeffrey Donaldson said it is "important that the Army retains the capacity to assist the police if required."

Sinn Fein MP Conor Murphy, the Regional Development Minister, said he was happy to see the end of the operation.

Employment Minister Sir Reg Empey, the Ulster Unionist leader, said: " The people of Northern Ireland owe a debt of profound gratitude to the Army."

The PSNI paid tribute to the Army for its help in creating the conditions which made possible the political progress and the changes seen in society.

A spokesperson said: "It could not have been done without the unstinting support and courage of our friends and colleagues in the Army.

"Throughout the darkest and most distressing times over more than 30 years, when police needed support, the soldiers of the British Army were there."

He added: "Thankfully police officers can now police with the community without the need for soldiers to protect them doing their normal job.

"That situation was a long time coming and we now look forward to working closely with all communities to ensure a safer Northern Ireland."